1. Field of the Invention
This invention relates to a method of producing .alpha.,.omega.-dialdehydes containing 8 to 12 carbon atoms and more particularly to a method of producing an .alpha.,.omega.-dialdehyde of 8 to 12 carbon atoms which comprises hydroformylating an .alpha.,.omega.-diolefin of 6 to 10 carbon atoms or an .alpha.,.omega.-alkenal of 7 to 11 carbon atoms and extracting the resulting reaction mixture.
The .alpha.,.omega.-dialdehyde of 8 to 12 carbon atoms, which is obtainable in accordance with this invention, is a compound of great use as an immobilizing agent for proteins and enzymes, a germicide, a high polymer crosslinking agent, or a strting material for the synthesis of the corresponding dicarboxylic acid, diol or diamine.
2. Description of the Prior Art
It is known that an .alpha.,.omega.-dialdehyde can be produced by hydroformylating an .alpha.,.omega.-diolefin or .alpha.,.omega.-alkenal of 6 to 10 carbon atoms with a mixture of hydrogen and carbon monoxide in the presence of a tertiary phosphine-modified rhodium compound as a catalyst. Because the rhodium catalyst used for this hydroformylation reaction is expensive, the commercial working of this known method calls for the separation of the rhodium catalyst from the product .alpha.,.omega.-dialdehyde for re-use, without entailing its loss and inactivation, in the subsequent hydroformylation reaction. In order to separate the rhodium catalyst from the product .alpha.,.omega.-dialdehyde by distillation, the reaction mixture must be heated to a high temperature, as high as to distill the highboiling .alpha.,.omega.-dialdehyde. Therefore, the rhodium catalyst undergoes pyrolysis in the course of distillation to cause precipitation of rhodium metal or degradation of the catalyst by byproduct high-boiling compounds so that the distillation residue containing the catalyst cannot be reused by recycling for a sufficiently long time. Therefore, as a method for avoiding the inactivation of the rhodium catalyst in separating it from the .alpha.,.omega.-dialdehyde following the hydroformylation reaction, it has been proposed to extract the hydroformylation reaction mixture (for example, U.S. Pat. No. 4,248,802, Japanese Patent Application Laid-Open No. 21638/1983, No. 157739/1983, No. 216138/1983) Japanese Patent Application Laid-Open No. 167937/1982 (corresponding to U.S. Pat. No. 4,248,802) discloses a method which comprises hydroformylating a functional group-containing mono or other olefine in water or a hydrous solvent using a water-soluble sulfonated phosphine and separating the product aldehyde by decantation or extraction. Further, Japanese Patent Application Laid-Open No. 157739/1983 and No. 216138/1983 each teaches a method which comprises hydroformylating 7-octen-1-al, 1,5-hexadiene or 1,7-octadiene in an aqueous solution of sulfolane or 1,4-butanediol in the presence of a water-soluble sulfonated phosphine and extracting the reaction mixture with a higher alcohol or a mixture thereof with a hydrocarbon. It is described therein that by the above method the infiltration of the catalyst and reaction solvent into the extract can be prevented and that only the straight-chain .alpha.,.omega.-dialdehyde can be selectively extracted and separated as the hemi-acetal of the higher alcohol. Further, Japanese Patent Application Laid-Open No. 21638/1983 teaches a method which comprises hydroformylating .alpha.,.omega.-diolefin, .alpha.,.omega.-alkenal or the like ih a water-insoluble organic solvent such as toluene and contacting the resulting reaction mixture with an aqueous solution of alkali metal hydrosulfite such as sodium hydrosulfite. By this procedure, the .alpha.,.omega.-dialdehyde produced by hydroformylation is selectively extracted into the aqueous layer as the alkali metal hydrosulfite adduct.
It is stated in Japanese Patent Application Laid-Open No. 167937/1982 (U.S. Pat. No. 4,248,802) referred to above that functional group-containing monoolefins and other olefins can be used as starting compounds but this literature does not contain specific reference to the use of .alpha.,.omega.-diolefins containing 6 to 10 carbon atoms or 60 ,.omega.-alkenals containing 7 to 11 carbon atoms. The research conducted by the present inventors showed that when these .alpha.,.omega.-diolefins or .alpha.,.omega.-alkenals are used as reactants, the hydroformylation method described in Japanese Patent Application Laid-Open No. 167937/1982 (U.S. Pat. No. 4,248,802) does not give satisfactory results. Thus, since the starting material .alpha.,.omega.-diolefin or .alpha.,.omega.-alkenal is sparingly soluble in water, the hydroformylation reaction hardly proceeds when water is used as the reaction solvent, for the contact between the starting material and the rhodium catalyst dissolved in water is poor. When a mixture of water and a water-miscible organic solvent is used as the reaction solvent, the hydroformylation reaction rate can be improved by increasing the solubility of .alpha.,.omega.-diolefin or .alpha.,.omega.-alkenal in the reaction solvent. However, it has been found that when the hydroformylation of an .alpha.,.omega.-diolefin or .alpha.,.omega.-alkenal is conducted in a homogeneous reaction system using a mixture of water with an organic solvent (such as ethyl alcohol, acetone, acetonitrile, dimethoxyethane etc.) as specifically mentioned in Japanese Patent Application Laid-Open No. 167937/1982 (U.S. Pat. No. 4,248,802), the reaction proceeds anyway but when the reaction mixture is extracted with any of the solvents specifically mentioned (diethyl ether, benzene or toluene) in the same patent literature, the reaction solvent and catalyst find their way into the extract in large quantities to preclude a selective extraction of the desired product .alpha.,.omega.-dialdehyde. If a large amount of the catalyst component is extracted along with the desired product in such an extraction process, the subsequent distillative process for the purification of the product from the extract entails the inactivation of the extracted catalyst, so that such a production system is quite disadvantageous for commercial implementation. In order that the hydroformylation and subsequent extractive separation of the product from the catalyst may be advantageously accomplished on a commercial scale, it is necessary to find a suitable combination of a reaction solvent which is capable of assuring a sustained commercially satisfactory reaction rate for the hydroformylation of a specific olefin with an extractant which is capable of selective separation of the hydroformylation product.
The methods described in Japanese Patent Application Laid-Open No. 157739/1983 and No. 216138/1983 each comprises carrying out the hydroformylation of an .alpha.,.omega.-diolefin or .alpha.,.omega.-alkenal and the subsequent extraction and separation of the straight-chain .alpha.,.omega.-dialdehyde from the reaction mixture using a combination of a certain reaction solvent with a certain extractant and as such provides advantageous procedures for the production of straight-chain .alpha.,.omega.-dialdehydes. However, these methods of necessity call for subjecting the hemiacetal essentially composed of higher alcohol and the straight-chain .alpha.,.omega.-dialdehydes to distillation after extraction to decompose to .alpha.,.omega.-dialdehyde and, as a consequence, not only requires a step for recovery of the higher alcohol but entails partial conversion of the .alpha.,.omega.-diadehyde to the acetal compound in the course of distillation, thus tending to lower the yield of the .alpha.,.omega.-dialdehyde.
The method described in Japanese Patent Application Laid-Open No. 21638/1983 requires a time-consuming step for decomposition of the alkali metal hydrosulfite adduct in the separation of the desired .alpha.,.omega.-dialdehyde from the aqueous layer of the extract and entails a large consumption of alkali metal hydrosulfite, thus being economically disadvantageous.